In the operation of conventional spiral classifiers for the separation of ore or sand particles according to particle size water is introduced together with the material to be processed as a slurry mixture into an elongated classifier tank. The classifier tank is an upwardly inclined, trough-like apparatus whose upper end is open and whose lower end is closed by a weir plate. A raking mechanism in the from of a motor-driven spiral-ribbon extends along the length of the tank to agitate the process material and to induce movement of the coarse fraction deposited on the floor of the tank generally in the direction of the upper end of the tank. Although solids separation is affected by several factors it is primarily dependent upon the time required for the particles to gravitate to the bottom of the liquid pool within the tank such that the coarse solids fraction is discharged from the upper, open end of the tank while the fine solids fraction passes over the weir plate at the lower end thereof.
In the application of spiral classifiers for the size separation of the tailings from certain ore beneficiating processes undesirable results have been obtained in that the coarse fraction discharged from the apparatus contains undue amounts of free mositure. The large amounts of liquid contained in the discharge excessively burdens the conveying system which conducts the material discharge to storage hoppers from which it is loaded onto trucks for ultimate disposal. It further potentially causes problems in the motor and drive systems of the trucks used to carry the material as well as increasing the maintenance requirements on the conveyor systems and the pocket seals employed in both the trucks and the storage hoppers. Lastly, it increases the bulk density required to be handled by both the trucks and the conveyor systems with an attendant increase in the cost of operating the processing system.
It is to the improvement of the operation of such spiral classifiers therefore that the present invention is directed.